You know, StartPage is basically just a proxy for Google - you get the same results, just without the tracking (attempts) and blocks. Using their search engine is good for them, since it bumps its popularity and ad view count, so I like to use it whenever I'm in Tor.
– JamesTheAwesomeDudeNov 2 '13 at 15:01

1

I did find some governmental and legal sites such as commercal register in Germany that do check the usage of TOR and they tell you, that such access is blocked.
– user615Dec 4 '13 at 8:25

@mirimir Then bots would use Tor to search google to harvest results and overload Google servers. I see no reason why they should take the risk.
– UfoguyDec 4 '13 at 15:40

3

Use startpage.com instead. It's an anonymous layer on top of Google that is recommended by the Tor.
– get52Feb 17 '14 at 20:56

4 Answers
4

In this case, Google is not interested in the fact that you are using Tor. Google runs some analysis on search queries and they sometimes produce this result.

The background is that Google has to deal with all sorts of abuse; for example, some people send lots of queries in a short timespan to overload the servers. Google checks for this and presents the warning in your question. This can happen when you use Tor, but also when your company uses a central proxy and when lots of users Google at the same time.

In your case, many Tor users probably used the exit to send a search query to Google. Their algorithms flagged that as suspicious, and so you get this message. In the second case, you have the chance to present yourself as a human (solving the captcha) and Google will process your query.

Normally this behaviour changes when your Tor circuit changes. I don't see this very often. However, you can also use an alternative search engine like Bing or DuckDuckGo.

Google (and any other website) has the ability to know that you are a Tor user because the list of Tor exit relays is public.

Google (and any other website) has the ability to know that you are using Tor Browser because of it's browser fingerprint.

Should I do something at my end.

No. Nothing to worry about because of this.

Google's automated abuse prevention systems only "think" it's better to prevent access in this case. (Those abuse prevention systems probably do neither make of use ability 1. or 2.) This is because, too many people are sharing the same Tor exit relay and the abuse prevention systems "think" it is automated access.

Either use Tor Browser's new identity feature and check if that helps or use another search engine.

Google has the ability to know that your are using Tor but I do not think that they are actually checking your IP address in the Tor exit relays list for common traffic.
– paboukOct 4 '13 at 12:04

Google has supported Tor and other anonymity/privacy friendly projects (e.g., Tahoe-LAFS) through its Summer[s] of Code. Also, Google staff have posted supportively on tor-talk.
– mirimirOct 9 '13 at 3:39

@pabouk There are different ways to answer this question. I don't think that the actual google system deciding to show "we are sorry" uses the information if Tor is being used or not into its calculation. On the other hand, I would be surprised, if none of google's systems do analyize IP addresses and fingerprints. They have the ability to know it, that is right and I wanted to point that out.
– adrelanosOct 10 '13 at 5:52

It is easy for any website owner to know you are using Tor because the list of Tor exit nodes is publicly available. Google has said they are not specifically targeting Tor users by making them solve captchas. Rather it is because each exit node sends so much traffic to Google that the traffic patterns seem similar to those of a bot, which would also send a lot of traffic to Google at once. See also: https://www.torproject.org/docs/faq.html#GoogleCAPTCHA

I do not think that Google is actively detecting if a connection arrived through the Tor network. See the earlier answers.
– paboukOct 4 '13 at 12:07

@pabouk indeed, probably not in the spam detection system. On the other hand, I would be surprised if Google isn't working on making use of browser fingerprints and other interesting information (such as connections coming from a Tor exit). See my answers and its comments for more.
– adrelanosOct 10 '13 at 6:03

@adrelanos: I did not wrote it exactly as I wanted. I rather wanted to say that CAPTCHA is not probably a direct result of the fact that you connected through Tor. I would agree that in some situations they probably use the information that the connection is coming from a Tor exit.
– paboukOct 10 '13 at 7:13